Mediation is a way of resolving issues without going to court. With skills and training, the mediator can help the parties resolve their issues with a minimum of conflict and antagonism, creating an agreement that meets their respective needs.
Usually, the parties participate without lawyers, although they are encouraged to have independent counsel, and may elect to have lawyers present. Mediation may occur before a case has been filed, and at any time during a case.
In California, there are no standards for mediators, no licensing of the profession, and no certification process. Someone claiming to be "certified" as a mediator is not certified by any state agency, if at all. Your dry cleaner is legally qualified to mediate your divorce, custody case, or other important issues - he may have taken a class in Mediation, which certifies that he attended, but that does not make him competent. The mediator should be able to teach you the law in a complicated field, have learned to avoid bias, and assist in exploring various alternative solutions. Preparing a contract as a result of the Mediation or advising you on the law is the practice of law - only lawyers may do so, not "paralegals" or people claiming to be mediators.
It is important you evaluate your potential mediator based on his or her experience in the field of law, and the quality and level of training in Mediation and Alternate Dispute Resolution. Each lawyer on this site is a Certified Specialist in Family Law, well trained and educated in the matters they mediate - they are more than capable of explaining the law, your rights and responsibilities. As litigators with decades of court room experience, they can tell you what judges are likely to do in cases like yours, and help you understand why the adversarial system may not be in your best interest.
With motivated parties, Mediation is often the least expensive and fair way of resolving your issues, both financially and emotionally.